Apparatus and method for automatically controlling the removal of excess coating from running lengths of material



y 1956 H. TAYLOR ET AL 3,251,710

APPARATUS AND METHOD FOR AUTOMATICALLY CONTROLLING THE REMOVAL OF EXCESS COATING FROM RUNNING I LENGTHS OF MATERIAL Filed March 4, 1963 3 Sheets-Sheet 2 1 50 -60 62 1/11 5/ M SOURCE I I I I I L ,eau. PRESSURE DRIVE MECHANISM May 17, 1966 H. TAYLOR ET AL 3,251,710

APPARATUS AND METHOD FOR AUTOMATICALLY CONTROLLING THE REMOVAL OF EXCESS COATING FROM RUNNING LENGTHS OF MATERIAL j 3 Sheets-Sheet 5 Filed March 4, 1963 United States Patent APPARATUS AND METHOD FOR AUTOMATICAL- LY CONTROLLING THE REMOVAL OF EXCESS COATING FROM RUNNING LENGTHS 0F MA- TERIAL Harold L. Taylor, Hammond, Ind., and Rodger L. Winn, Ann Arbor, Mich., assignors to Inland Steel Company, Chicago, 111., a corporation of Delaware Filed Mar. 4, 1963, Ser. No. 262,499 10 Claims. (Cl. 117-102) This invention relates to coating applications, and more particularly to a method and apparatus for applying'coatings to a continuous strip or web. In its more specific aspect, this invention relates to a method and apparatus for controlling coating applications to a strip in a continuous dip-coating process.

The words strip or web are used herein to denote a continuous lengh.

In dip-coating operations wherein a strip or web to be coated is continuously passed through a bath of coating material, it is necessary to control the thickness and/ or Weight of the coating applied to the strip. The purpose of the control is to obtain a uniform coating, and equally important, minimize loss and waste of coating material. Generally, this control necessitates measuring the coating thickness of a sample cut trom the strip, and, if required, adjusting the coating operations. This method is undesirable from an economical and operational standpoint because of the time required in making this measurement. Because of this time lag any error in the coating thickness is prolonged before being detected. It therefore would be advantageous to minimize any error by employing a more rapid means for detecting coating thickness error and taking corrective action.

In accordance with the present invention for controlling coating applications to a continuous strip or web, the strip is contacted with the coating material, such as by passing the strip through a bath of coating material contained in a suitable vessel. The strip is then passed through a suitable coating control means, for example, a coating roll means, which is adjustably positioned to permit passage therethrough of a coated strip of predetermined quantity, e.g., thickness and/or weight. To accomplish this, the coating material applied per unit area of strip is continuously measured. In the preferred embodiment of the invention, the rate of change of liquid level of coating material in the vessel is continuously measured to determine the quantity of coating material applied to the surface of the strip. Simultaneously, the area of strip being coated is determined by measuring the strip width and speed. In this manner, the coating applied per unit area of strip is readily determined. This result is compared with a reference standard of predetermined quantity, and any difference between the actual coating applied and the reference standard is detected. This difference is corrected by adjusting the coating control means, as explained in greater detail hereafter. In this manner, the coating operation is controlled continuously to obtain a coating application of predetermined quantity, e.g., thickness and/or weight. Any error in coating applied is minimized by substantially reducing the time lag involved in making the coating measurement and in taking corrective action.

The invention is described herein below in greater detail with reference to galvanizing a ferrous strip, or sheet, such as low carbon steel, with zinc by a continuous dip-coating process. In the accompanying drawings:

*FIGURE 1 is a diagrammatic view of the system of the present invention, the control mechanism being illustrated schematically;

. FIGURE 2 is a sectional view showing a galvanizing "Ice pot as employed in accordance with the invention, and showing details of an elevator means for adjusting the coating rolls;

\FIGURE 3 is an elevational view on line 33 of FIG- URE 2 to show details of the worm screw of the elevator means;

FIGURE 4 is a diagrammatic view showing in detail a control means employed in adjusting the passage between coating rolls; and

FIGURE 5 (is an electrical circuit diagram illustrating the control system employed in connection with the elemen-ts of the preceding figures.

Referring to the drawings wherein like reference numerals designate similar parts throughout the various views, there is shown a galvanizing vessel or pot for containing molten zinc 1111 and havingmounted therein sinker roll 12. Metal strip 14, to be coated with zinc, is drawn in the direction indicated by the arrow through the molten zinc bath and over roll \12. As the strip leaves the .bath, it is passed through a suitable coating roll assembly indicated generally by the numeral 16. There is illustrated as exemplary of asuitable coating roll assembly a pair of horizontally positioned rollers 18 and 20 having their longitudinal axes parallel to each other and a roll center line substantially parallel to the liquid level of the bath. Rollers =18 and 20 are positioned to permit passage therethrou gh of the coated strip, and are suitably adjusted such that the rolling pressure, or nip-pressure, applied to the coated strip passing there- 7 through may be regulated. A coating application is controlled upon proper adjustment of the roll center line relative to the liquid level of the bath and the nip-pressure, as described herein below in greater detail.

In describing the coating roll assembly in' greater detail, and referring in particular to FIGURES 2 and 3,

there is shown a suitable elevator means, indicated generally at .22, comprising a worm drive vertical lift screw and a base 24 for supporting the elevator means. Motor unit *26 for driving worm gear 28 through shaft 30 is energized by a selector circuit '32, described hereafter in detail. Threaded stem 64 is rigidly connected to the worm gear for rotation, and extends through threaded nut 36 which is keyed in plate member 38 to hold the nut against rotation. The threaded stem is secured at its upper end by a suitable cross head 40, and plate member '38 is supported by bracket means 42. Rail 44 is adapted to slide in guide gibs 46 which are grooved to provide a sliding tongue and groove connection between the gib and rail and to permit vertical movement of plate member 38. Extending transversely from plate member '38 are opposing arms 48, and rolls 1-8 and 20 are journalled at their horizontal axes by the arms. Thus, rotation of worm gear 28 rotates stem 34 for effecting vertical movement of plate member 38 which in turn moves arms 43. Accordingly, an appropriate signal transmitted to selector circuit 32 to roll level drive mechanism 49 actuates motor unit 26 for driving the worm drive vertical lift screw, described below in more detail, thereby adjusting the roll center line position of rollers 18 and 20 relative to the liquid level of the bath.

The rolling pressure, or nip-pressure, exerted on the strip between the rollers 18 and 20 is controlled by a suitable pneumatic or hydraulic means as shown more specifically in FIGURE 4. For this purpose, roll 18 is journalled in the lower ends of opposing levers '50 which are pivotally mounted intermediate their lengths at 51. In this manner, roll 18 is adjustably mounted relative to roll 20. The opposite end of each of levers 50 is connected to a linking member 52 actuated by a suitable piston 54 cooperatively arranged in cylinder 56. Piston 54 is spring biased by coil spring 58 in the direction 3 of decreased rolling pressure. Air, or other suitable fluid, is admitted to the cylinder through line 60 from regulator means 62 having a suitable source (not shown) to bias the piston in the opposite direction. A suitable regulator lator means 62 and the force exerted by coil spring 58 i may be predetermined, such as for example a zero signal from selector circuit 32 would provide pressure necessary for mid-range rolling pressure.

During the galvanizing process, the zinc coating material contained in the galvanizing vessel is depleted, and consequently the liquid level of molten zinc decreases. In accordance with the present invention, the liquid level of coating material is continuously measured by a liquid level sensing device. For this purpose a sensing device 64, composed of a material substantially inert to the coating composition and which is resistant to attack by the molten zinc, is immersed in the bath. There is shown in FIGURE 1 as a suitable sensing device a cylindrical member composed of graphite closed at the bottom and having a longitudinal bore 66 extending through. the cylinder'to the bottom wall. The sensing device is provided with a suitable outlet 68 extending laterally from longitudinal bore 66, and upon immersion in the coating bath, provides communication between the longitudinal bore 66, and the interior of the galvanizing vessel 10 below the liquid level of molten zinc. In this manner, a gas which is inert to the coating compositionis introduced to the molten zinc bath from a source not shown via a line 70, a longitudinal bore 66 and outlet 68, and bubbles to the surface of the bath. The rate of flow of gas introduced to the molten bath is automatically controlled at a constant value by pressure regulator 72 and flow control meter 74, both of which are incorporated in line 70. Suitable gases include the inert or reducing gases, for example, nitrogen, argon, hydrogen, natural gas, carbon dioxide, etc. 7

The distance from outlet 68 of sensing device 64 to the surface of molten metal is indicated by the letter L.

(See FIGURE 1). When gas is introduced to the moiten bath, the back pressure, or level indicating pressure, in the sensing device is measured. This pressure is a measure of the liquid height L, L being equal to the measured pressure divided by the specific weight of the coating material. This back pressure actuates a dilferential pressure transducer 76. Transducer here is used in the broad sense or pressure actuated switch. Recorder 78 may be of the a predetermined liquid level, the power output from transducer 76 declines whereby switch means 80 is actuated to the fill position and motor 83 is energized- Conveyor belt 82, laden with zinc, is driven in the direction indicated by the arrow whereby zinc is added to the bath, When sufiicient zinc has been added to increase the power output from transducer 76, switch means 80 is actuated to the opposite, or stop, position to de-energize the motor thereby stopping the conveyor. When desired, a hopper may be employed having a power actuated outlet, actuated to open and closed positions by switch -means 80. vAs a further alternative, switch means 80 may energize an audible or visual signal for manual addition of zinc to the bath. In this manner, the liquid level of the coating bath may be manually maintained within a predetermined range. 7

During the coating operation, the value of L decreases as the metal coating is applied to the strip. With each incremental decrease in L, there is a decrease in the level indicating pressure transmitted to transducer 76. The power output from the transducer is supplied also to second transducer 84, and as this output decreases, the output from transducer 84 will be a decreasing current,

which rate of decrease with time is determined by dif- 1 entiator 86 is directly proportional to the rate of decrease in liquid level of the molten bath. This rate of decrease in liquid level is proportional, to the coating material applied to the strip per unit of time. p

In order to determine the average coating weight applied per unit area of strip, it is necessary to measure the surface area to be coated per unit of time. As a means for taking this measurement, there is provided a suitable counter means 88, such as a line speed tachometer,

to measure the length of strip fed to the coating bath per unit of time, and a potentiometer -which is set to simulate the particular strip width employed in the process. The counter means 88 may be a conventional line speed transmitter as shown in Foxboro Bulletin 563, page B49, and further disclosed in Control Engineers Handbook, page 12.67, McGraw-Hill, first edition, 1958. The potentiometer 90 for measuring strip width may be of the type shown in the Foxboro Company Technical Information Brochure 39-151a" dated November 20, 1962. Appropriate signals from the counter means and potentiometer are transmitted to a suitable mulitplier 92 wherein these signals are multiplied to obtain the surface area coated per unit of time.

It will be observed that the average coating weight per unit area is obtained by the following formula:

Coating material applied Strip area coated In order to obtain the average coating weight, signals from diiferentiator 86 and multiplier 92 are transmitted to a suitable divider circuit94. The resulting signal from the divider, circuit is recorded on a continuous recorder 96 substantially of the same type as recorder 78, which indicates directly the average coating weight applied to the strip. A suit-able multiplying circuit is shown in Control Engineers Handbook, pages 5-11, figure (a), Mc- Graw-Hill, first edition, 1958. Themultiplier and divider of the type that may be employed for use in this inven tion are further described in the Foxboro Technical Information Brochure 39-l64a, dated November 1, 1961. In accordance with the preferred embodiment of the invention, the coating weight applied to the strip is controlled automatically. In the control network there is provided a potentiometer 98 connected to a suitable power source (not shown) which is set manually to simulate a strip bearing a coating weight of predetermined or -desired value. The potentiometer provides a reference standard, the signal from which is supplied to a comparer circuit 100 where it is compared with the signal from divider circuit 94 which is a function of the actual coating weight achieved. Comparer circuit 100, including potentiometer 98, of the type suitable for use in this invention is adequately described in Process Instruments and Controls Handbook, by Douglas M. Considine, pages 9-68 and 9-69, McGraw-Hill, L957. The output error signal from comparer circuit 100 is proportional to the difierence between the actual coating weight and the desired coating weight, and this signal is transmitted to selector circuit 32 for actuating the coating roll assembly 16. Depending on the magnitude in difference between the actual and desired coating weight, the coating roll assembly may be adjusted for changing the roll center line position relative to the liquid level of the bath and/or changing the pressure of the rollers 18 and 20 exerted against the coated strip.

Selector circuit 32 is set to distinguish the magnitude of error which is arbitrarily established as large or small, depending upon the requirement of the coating operation. In addition, the polarity of the output error signal is measured to indicate in which direction the error lies; that is whether the coating application is heavier (thicker) or lighter (thinner) than required. A large error in coating weight is more readily corrected by suitable adjustment of the roll center line; whereas, a small error is more readily corrected by adjustment of the rolling pres sure. For example, a large error having a positive polarity detected in the selector circuit is transmitted to the roll level drive mechansm 49 which energizes motor unit 26 and in turn drives the elevator means 22 to raise the coating roll assembly, thereby adjusting the roll center line position relative to the liquid levelto corect for the error. On the other hand, a large error having a negative polarity would lower the coating roll assembly. Similarly, a small error having a positive polarity detected by the selector circuit is transmitted to the roll pressure drive mechanism 63 to actuate the piston 54 thereby adjusting the pressure of the rollers 18 and 20 against the strip in the direction of increasing pressure. The roll pressure would be decreased if a small error having a negative polarity were detected.

In FIGURE 5, there is shown an electrical circuit arrangement fed by a suitable power source (not shown) for controlling the coating roll assembly, but other suitable designs may be employed. As explained above, comparer circuit 100 transmits an output error signal which may be represented as the potential between the terminals and is proportional to the difference between the actual coating weight and the desired coating weight. At the beginning of the coating operation, each switch or contact is in the position indicated. Assuming a relatively large error signal is transmitted from the selector circuit, current 'enters the circuit and energizes relay 108 which is actuated to a closed position. Relays 110 and 112 and polarized relay 114 are similarly energized and the corresponding switches actuated to a closed position. Roll level drive mechanism 49is actuated thereby energizing motor unit 26; and, depending on the polarity of the error signal, elevator means 22 is adjusted in the proper direction. The circuit will remain closed until the output error signal declines to a predetermined value, at which relays 110 and 112 and polarized relay 114 will be deenergized, as well as relay 108 which is actuated to an open position thereby terminating the control signal to the roll level drive mechanism 49. On the other hand, where the output error signal is relatively small and in-. sufficient to energize relay 108, polarized relay 116 is energized, and, depending on the polarity of the error signal, roll pressure drive mechanism 63 is actuated to adjust the pressure of the rollers against the strip. When the error signal has been corrected, relay 116 is de-energized and the switch actuated to an open position.

In another embodiment of the invention, the selector circuit 32 for automatically controlling the coating weight may be omitted and the operation controlled manually. An operator may observe from recorder 96 the average coating weight applied to the strip, and accordingly may adjust the coating roll assembly 16 by manual means.

Our invention is particularly advantageoustin that we provide apparatus and method for rapidly adjusting coating applications to the strip. By reason of the invention, the operations are performed with minimum time lag and the rapid-control response eliminates losses in coating material and strip.

It should be understodod that the present invention is applicable to other coating applications and the coating of other materials. Thus, for example, the invention may be used for controlling the coating applications of other metals, such as aluminum, foil or sheet, paper, cloth and plastics; and may be used in applying adhesive or plastic coatings to a suitable substrate, as well as decorative or protective coatings.

The foregoing detailed description has been given for clearness of understanding only, and no unnecessary limitations should be understood therefrom, as modification will be obvious to those skilled in the-art.

What is claimed is:

1. A method for cont-rolling a coating application to a continuous strip, comprising:

(a) continuously contacting said strip with a coating material;

(b) passing said strip through an adjustable coating control means which is adjustably mounted relative to the zone of contact of said coating material with said strip to exert pressure on the coated strip;

(c) continuously measuring the coating material applied to said strip, and continuously measuring the area of said strip being coated whereby the coating material applied per unit area of said strip is determined; and

' (d) adjusting the pressure exerted by said'coating con trol means and the position of said coating control means relative to said zone of contact to obtain a coating of predetermined quantity.

2. A method for controlling a coating application to a continuous strip, comprising:

(a) continuously passing said strip through a bath of coating material to be applied to the surface of said strip;

(b) passing said strip through an adjustable coating roll means which is adjustably mounted relative to the liquid level of said bath for exerting pressure on the coated strip;

(c) continuously measuring the liquid level of said bath, the rate of change of said level being proportional to the coating applied to said strip, whereby the coating applied per unit area of said strip is determined; and.

(d) adjusting the pressure exerted by said coating roll means and the position of said coating roll means relative to said liquid level of said bath to obtaina coating of predetermined quantity.

3. A method according to claim 2 wherein said determined measurement of coating applied per unit area of said strip is compared to a reference standard simulating a coating application of predetermined quantity, said comparing distinguishing the magnitude of any difference between said coating applied and said reference standard, and adjusting'said coating roll means relative to said liquid level to correct for a difference greater than or equal to a certain arbitrarily selected value, and adjusting said pressure exerted to correct for a difference less than or equal to said selected value.

4. A method for controlling a coating application to a continuous strip, comprising:

(a) continuously passing said strip through a bath of coating material to be applied to the surface of said strip, said bath having immersed therein a liquid level sensing means;

(b) passing said strip through an adjustable coating control means which is adjustably mounted relative to the liquid level of said bath for exerting pressure on the coated strip;

(0) continuously introducing gas substantially inert to said coating material to said bath through said liquid level sensing means whereby a back pressure is established in said sensing means;

(d) continuously correlating the rate of change of said back pressure to the coating weight applied, and continuously measuring the area of said strip being coated, whereby the coating applied per unit area is determined; and

(e) adjusting the pressure exerted by said coating control means and the position of said coating control means relative to said liquid level of said bath until said back pressure records a predetermined value to obtain a coating of predetermined quantity.

5. A method according to claim 4 wherein coating material is added to said bath when said back pressure records a second predetermined value to maintain the liquid level of said bath within a predetermined range.

6. Amethod for controlling a zinc coating application to a ferrous strip, comprising:

(a) continuously passing said strip through a-bath of molten zinc to be applied to the surface of said p; a

(b) passing said strip through a plurality of adjustable rollers for exterting pressure on the coated strip and having a roll center line subtsantially parallel with the liquid level of said bath and adjustably mounted relative to said liquid level;

(c) continuously introducing gas which is inert to said molten zinc to said bath through a liquid level sensing device adaptable for immersion in said bath, whereby a back pressure is established in said sensing device;

(d) continuously correlating the rate of change of said back pressure to the coating weight applied and continuously measuring the area of said strip being coated, whereby the coating applied per unit area is determined;

(e) adding zinc to said bath when said back pressure records a predetermined value to maintain the liquid level of said bath within a predetermined range; and

(f) comparing the measurement of coating applied per unit area to a reference standard simulating a coating application of predetermined quantity, and distinguishing the magnitude of any ditference between said coating applied and said reference standard, and adjusting said rollers relative to said liquid level to correct for a difference greater than or equal to a certain arbitrarily selected value, and adjusting said pressure exerted by said rollers to correct for a difierence less than or equal to said selected value.

7. Apparatus for controlling coating applications to a continuous strip, comprising:

(a) a vessel for containing a coating material;

(b) adjustable coating roll means for exerting pressure on the coated strip and adjustably mounted relative to the liquid level of said coating material contained in said vessel;

(c) means for passing said strip through said coating material contained in said vessel and through said coating roll means;

(d) means for continuously measuring the liquid level of said coating material in said vessel, the rate of change of said level measurement being proportional to the coating applied to said strip, and means for continuously measuring the area of said strip being coated, whereby the coating applied per unit area of said strip is determined;.and

(e) means responsive to said measuring means for adjusting the pressure exterted by said coating 1011 means and the position of said coating roll means relative to said liquid level, whereby a coating of predetermined quantity is applied to the, strip.

8. Apparatus according to claim 7 including means for continuously comparing the determined measurement of coating applied per unit area of said strip to a reference standard simulating a coating application of predetermined quantity, means for distinguishing the magnitude of any difference between said determined measurement of coating applied and said reference standard, and said responsive means includes means for adjusting said coating roll means relative to said liquid level to correct for a difference greater than or equal to a certain arbitrarily selected value, and adjusting said pressure exerted to correct for a difference less than or equal to said selected value.

9. Apparatus for controlling coating applications to a continuous strip, comprising:

(a) a vessel for containing a coating material;

(b) adjustable coating roll means for exerting pressure on the coated strip and adjustably mounted relative to the liquid level of said coating material contained in said vessel;

(c) means for passing said strip through said coating 'material contained in said vessel and through said coating roll means;

(d) a liquid level sensing means adaptable for immersion in said coating material for continuously measuring the liquid level of said coating material in said vessel having a power output proportional to said liquid level, the rate of change of said liquid level measurement being proportional to the coating applied to said strip, and means for continuously measuring the area of said strip being coated, whereby the coating applied per unit area of said strip is determined; 7 i

(e) feeder means adapted to replenish said coating material to said vessel;

(f) actuating means responsive to the power output from said liquid level sensing means for operating said feeder means; and p (g) means responsive to the power output from said liquid level sensing means for adjusting the pressure exerted by said coating roll means and the position.

of said coating roll means relative to said liquid level, whereby a coating of predetermined quantity is applied to the strip.

19. Apparatus for controlling a zinc coating applica tion to a ferrous strip, comprising:

(a) a vessel for containing molten zinc;

(b) a plurality of rollers having a roll center line substantially parallel with the liquid level of said molten zinc in said vessel and adjustably mounted relative to said liquid level, said rollers exerting pressure on the coated strip;

(c) means for passing said strip through said molten zinc contained in said vessel and through said rollers;

(d) a liquid level sensing means adaptable for immersion in said coating means forcontinuously introducing gas substantially inert to said molten zinc to said rbath through said liquid level sensing means,

whereby a back pressure is established in said sensing means;

(e) means for correlating the rate of change of said.

back pressure to the coating Weight applied, and

9 4 means for continuously measuring the area of said strip being coated, whereby the coating applied per unit area is determined;

(f) feeder means adapted to replenish zinc to said vessel;

(g) actuating means responsive to the back pressure output from said sensing means for operating said feeder means; and

(h) means responsive to the back pressure output for said sensing means for adjusting the pressure ex- 10 erted by said rollers and the position of said roll center line relative to said liquid level, whereby a Zinc coating application of predetermined quantity is applied to said istrip.

References Cited by the Examiner UNITED STATES PATENTS 928,385 7/1909 Huxley 118-429 2,841,111 7/1958 Walker 1187 2,914,419 11/1959 Oganowski 1171 14 2,977,925 4/1961 Norton 118 8 RICHARD D. NEVIUS, Primary Examiner.

JOSEPH B. SPENCER, Examiner. 

1. A METHOD FOR CONTROLLING A COATING APPLICATION TO A CONTINUOUS STRIP, COMPRISING: (A) CONTINUOUSLY CONTACTING SAID STRIP WITH A COATING MATERIAL; (B) PASSING SAID STRIP THROUGH AN ADJUSTABLE COATING CONTROL MEANS WHICH IS ADJUSTABLY MOUNTED RELATIVE TO THE ZONE OF CONTACT OF SAID COATING MATERIAL WITH SAID SRIP TO EXERT PRESSURE ON THE COATED STRIP; (C) CONTINUOUSLY MEASURING THE COATING MATERIAL APPLIED TO SAID STRIP, AND CONTINUOUSLY MEASURING THE AREA OF SAID STRIP BEING COATED WHEREBY THE COATING MATERIAL APPLIED PER UNIT AREA OF SAID STRIP IS DETERMINED; AND (D) ADJUSTING THE PRESSURE EXERTED BY SAID COATING CONTROL MEANS AND THE POSITION OF SAID COATING CONMEANS RELATIVE TO SAID ZONE OF CONTACT TO OBTAIN A COATING OF PREDETERMINED QUANTITY. 